The subject matter disclosed herein relates generally to active clearance control systems and, more specifically, to active clearance control systems that use compressor bleed air to pump fan bypass air for active clearance control using an air ejector, and associated methods.
Gas turbine engines feature several components, several of which define a core. With respect to the core, air enters the engine and passes through a compressor section which typically operates a set of compressor blades and stators arranged in stages. Each stage further compresses air that enters from an upstream stage. Some engine designs provide that the compressor stages are arranged with the initial stages being a low pressure compressor (LPC) and the remaining stages being a high pressure compressor (HPC). Upon being compressed as desired, the compressed air is routed through one or more combustors. Within a combustor are one or more nozzles that serve to introduce fuel into a stream of air passing through the combustor. Igniters are typically used to cause a resulting air-fuel mixture to burn within the combustor. The burned air-fuel mixture is routed out of the combustor through a turbine section to exert forces upon turbine blades thereby performing work. Some engine designs provide that the turbine stages are arranged with the initial stages being a high pressure turbine (HPT) and the remaining turbine stages being a low pressure turbine (LPT). In such designs, a system of axially concentric shafts is provided whereby the LPC is mechanically connected to the LPT and the HPC is mechanically linked to the HPT. For high-bypass turbofan engines, a bypass section has the largest blades that route some bypass air into the core, initially through the compressor, and remaining air outside the core, through a fan bypass duct, and alongside the engine where such bypass air rejoins the exhaust in the airstream downstream of an engine exhaust duct. The bypass section is often mechanically connected to the LPC. No matter the engine design selected, with the work extracted, the burned air-fuel mixture is routed out of the engine as exhaust.
In addition to the core and the components described above, aircraft turbine engines also utilize a cowl in order to route air in a desired manner. Active clearance control (hereinafter, ACC) has been utilized in order to provide impingement cooling of the casings under the cowl of the engine as a means to reduce blade tip clearances and achieve a positive effect on performance. Traditionally, an ACC system air inlet is located in a fan bypass duct, and an ACC exit vents to ambient pressure, such as that found outboard of the one or more nozzles within the core as described above. In other applications, such as, for example, marine or industrial turbines, ACC may be of even more importance and may be desired for operations at higher power settings than idle or partial power.
Some core components may be located in an axial position outside of the compressor, combustor, or turbine areas but inside a cowl outside of which bypass air flows. Such components are considered to be placed in an under cowl area. Core component cooling (hereinafter, CCC) refers to the routing of cold air along the outside of engine casings thereby keeping components within their design temperature limits. In addition, CCC can be utilized at low power settings or otherwise when there is not enough ambient air flowing through the cowl. For example, in aircraft applications, CCC has been found useful when the engine is being operated while the aircraft is on the ground running at idle or partial power. Once in flight, air flow is typically sufficient to cool the under cowl region.
The problems: For engines utilizing a long-duct-mixed-flow architecture, the fan bypass duct may extend past the core, and the inlet and outlet pressures may be approximately equal. Therefore, there may not be a large enough pressure difference available between inlet pressure and outlet pressure to drive desired ACC air flow. As a result, ACC system flow requirements may not be met. Further complicating such situations, direct HPC bleed may be too hot to provide desired cooling, and there may be insufficient space for direct LPC bleed tubing.